1. Field of the Invention
The present invention relates to an image forming apparatus forming an image on a sheet.
2. Description of Related Art
As an image forming method used for an image forming apparatus, there are a direct transfer system (for example, see Japanese Patent Application Laid-Open No. 7-295459) and an intermediate transfer system (see Japanese Patent Application Laid-Open No. 2004-240376).
In general, service men periodically perform replacement of consumables or maintenance of image forming apparatus at user's site. Recently, a design for the replacement or maintenance performed by users has been required. Therefore, processes of the image formation are designed to be implemented as individual units so that the units in the image forming apparatus can be detachably attachable by the users.
In addition, a jam clearance operation for the transfer material S (jammed paper) needs to be implemented. Japanese Patent Application Laid-Open Nos. 7-295459 and 2004-240376 discuss a construction where a position of a shaft pin in a fixing unit is determined with respect to an apparatus main body and an upper opening cover is opened or closed. In the construction, before the jam clearance operation is performed, the opening cover is rotated by manipulating a lever so as to open a conveyance path. After that, the jam clearance operation is performed.
In addition, Japanese Patent Application Laid-Open No. 10-187002 discusses a conveyance belt unit which is detachably attachable to the apparatus main body. More specifically, Japanese Patent Application Laid-Open No. 10-187002 discusses a construction where, when a conveyance belt unit is mounted on an apparatus main body, a key-shaped portion formed in the locking lever is engaged with a fastening shaft formed on the apparatus main body so that the conveyance belt unit can be held in the apparatus main body.
In such conventional constructions, if the opening cover or the conveyance belt unit is incompletely locked to the apparatus main body, the unit is not mounted on an accurate position, so that malfunction may occur in the image forming apparatus.